1. Field of the Invention
The present invention relates to a rolling bearing, a cam-follower with roller employing the rolling bearing, and a cam.
2. Description of the Background Art
Recently, demand for high-speed and high-load application of a full type roller bearing without cage such as a bearing for a rocker arm among rolling bearings has increased. In the present specification, the full type roller bearing and other rolling bearings are not particularly distinguished, and both are referred to as a rolling bearing herein. In the rolling bearing without cage, interference among rollers is inevitable, and a lubricant is not sufficiently supplied to the inside of the bearing. Accordingly, separation originating from a surface of a roller or a race may occur.
If the roller rotates with high speed, surface damage may occur in the roller due to assembly error or unbalanced load, or skew tends to be caused because a roller position is not smoothly controlled. As such, surface-originating separation due to slipping or internally originating separation due to local increase in surface pressure may take place. Consequently, heating due to slipping or local increase in surface pressure takes place, resulting in surface damage such as peeling, smearing or surface-originating separation or internally originating separation in spite of mathematically large load capacity.
Approaches shown below have been proposed in order to solve the above-described problems.
(1) In Japanese Patent Laying-Open No. 2000-38907, a bearing for cam-follower device for engine valve mechanism attains mathematically calculated life of the bearing of not less than 1000 hours at a rated engine speed.
(2) Japanese Patent Laying-Open No. 10-47334 discloses a bearing shaft for cam-follower device for engine valve mechanism in which carbide accounts for 10% to 25%, decomposition ratio of retained austenite to an initial value is set to 1/10 to 3/10, end face hardness is set to HV830 to 960, and average wavelength of surface roughness is set to not larger than 25 μm. In order to realize these characteristics, bearing steel is subjected to carbonitriding treatment and hard shot peening.
(3) Japanese Patent Laying-Open No. 10-103339 discloses a cam-follower shaft in which a solid lubricating film composed of high polymer or the like is formed on the shaft in order to improve abrasion resistance thereof.
(4) Japanese Patent Laying-Open No. 10-110720 discloses a cam-follower shaft manufactured from tool steel, for example, and attaining high hardness through ion nitriding or ion plating at a temperature lower than a tempering temperature.
(5) Japanese Patent Laying-Open No. 2000-38906 discloses a bearing for cam-follower device for engine valve mechanism, in which bending stress to a shaft is regulated to be not larger than 150 MPa.
(6) Japanese Patent Laying-Open Nos. 2000-205284 and 2002-31212 disclose a cam-follower for engine valve mechanism in which a phosphate coating having an excellent lubricant retaining property is applied to a rolling contact surface of a bearing component.
(7) Japanese Utility Model Laying-Open No. 63-185917 discloses a cam-follower for engine valve mechanism in which a roller rolling area of a shaft is crowned.
(8) Japanese Patent Laying-Open No. 2002-194438 discloses a shaft, in which a surface layer implementing a rolling contact surface of the shaft is subjected to high-concentration carburizing treatment or carbonitriding treatment in order to attain carbon concentration of 1.2% to 1.7% and an inner portion has a hardness of approximately HV300.
Meanwhile, when the cam-follower with roller in the engine is fixed to a rocker arm, opposite end faces of a shaft of the cam-follower are sometimes subjected to caulking forming so as to be caulked to a shaft support member. Here, the rolling contact surface of the roller should have high hardness, whereas the end portion should be soft so as to allow caulking forming. A number of developments taking into account such a characteristic have been made, as disclosed in Japanese Patent Laying-Open Nos. 5-321616 and 62-7908, and Japanese Patent Publication Nos. 6-15811 and 6-80287, for example.
In the future, however, tendency toward the use of the cam-follower with roller in the engine under higher speed and higher load conditions as well as lower viscosity of a lubricant is inevitable, as with an ordinary bearing. Here, improvement in rolling contact fatigue life under such condition of use is demanded.
An object of the present invention is to provide a rolling bearing that attains long life against surface damage such as surface-originating separation or internally originating separation under harsh condition of use and allows facilitated caulking work of an end portion, a cam-follower with roller employing the rolling bearing, and a cam.